Double-walled tubular heat exchanger

ABSTRACT

IN A DOUBLE-WALLED TUBULAR HEAT EXCHANGER, MORE PARTICULARLY CRYSTALLIZATION COOLER, HAVING SCRAPER BLADES WHICH ARE ARRANGED INTERNALLY AND ABUT AGAINST THE INNER WALL, AND WHICH ARE SECURED TO A ROTATABLE SHAFT EXTENDING IN THE AXIAL DIRECTION, THE IMPROVEMENT THAT FOR PRESSING THE SCRAPER BLADES AGAINST OR LIFTING THEM AWAY FROM THE INNER WALL OF THE   HEAT EXCHANGER THERE ARE ARRANGED BETWEEN THE BLADE HOLDERS AND THE SHAFT PNEUMATIC OR HYDRAULIC ADJUSTING DEVICES WHOSE PRESSURE MEDIUM CHAMBERS COMMUNICATE WITH AN EXTERNAL PRESSURE SOURCE THROUGH THE INTERIOR OF THE SHAFT.

United States Patent Inventor Wolihart Eisenmann [56] References CitedR'msburgi Gem"! UNITED STATES PATENTS PP 2 1969 892,424 7/1908 Holden165/94 d 1971 2,438,673 3/1948 McMahan 15/104.1x 22:3; 22; "vyss G m b H3,395,419 8/1968 Nunlist et al... l65/94X Rmmbm wumenberg, Germany3,430,928 3/1969 Smlth 165/94 Priority Sept. 6, 1968 PrimaryExaminer-Frederick L. Matteson Germany Assistant Examiner-Theophil W.Streule P 17 94 098,6 Attorney-Dodge and Ostmann DOUBLE-WALLED TUBULARHEAT EXCHANGER particularly crystallization cooler, having scraper QABSTRACT: In a double-walled tubular heat exchanger, more blades whichare arranged internally and abut against the inner wall,

schims4nnmng Figs and which are secured to a rotatable shaft extendingin the US. Cl. 165/94, axial direction, the improvement that forpressing the scraper 259/68, 15/ 104.05 blades against or lifting themaway from the inner wall of the lnt. CL F28g 3/12 heat exchanger thereare arranged between the blade holders Field of Search 165/87, 94, andthe shaft pneumatic or hydraulic adjusting devices whose 92;34/l24, 125;i5/l04.1, 104.1 (C), 104.09, 93, 104.05; 62/354; 118/204-205; 259/68(lnquir ed) pressure source through the interior of the shaft.

x 23 I IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII pressure mediumchambers communicate with an external PATENTEU JUN28 |97| SHEET 2 OF 2Fig.3

INVENTOR. Wo/fharfi [Zsenmarm ATTORNEYS DOUBLE-WALLED TUBULAR HEATEXCHANGER BACKGROUND OF THE INVENTION Double-walled, tubular heatexchangers, more particularly crystallization coolers, in whose interiorscraper blades are arranged which abut against the inner wall of theheat exchanger and are secured to a rotatable shaft extending in theaxial direction are known per se. They are used, for example, for thecontinuous cooling of a molten material which is solid at normaltemperature, and for converting the melt to a mass of crystals. In orderto ensure that the mass crystallizes as uniformly as possible throughoutand that flowable or pourable crystals are obtained instead of coherentblocks of crystals, it is necessary to stir the mass round continuouslyduring the cooling and crystallizing operation. The stirring means areusually constructed as scraper blades or helical elements, which has theadvantage that at the same time they move the mass forwards through thecooling apparatus.

To dissipate the crystallization heat which is evolved duringsolidification, a coolant is conducted through the space between the twowalls of the heat exchanger which are arranged coaxially one within theother. The coolant may be, for example, water at a suitable temperatureor a suitable brine which is appropriately temperature-controlled inaccordance with the nature of the material being processed.

Apparatus of this kind are shown for example in German patentspecifications Nos. 249,680 and 808,829. These publications also showthat the tubular heat exchangers are generally arranged horizontally,and a plurality of such apparatus can be connected in series with oneanother, the material to be cooled passing through them, for example, inzigzag manner.

When the melt is cooled within the heat exchanger, the heat released isdissipated by conduction. Since the tubular crystallization chamber iscooled from the outside, it is unavoidable that the cooling processproceeds most quickly in the vicinity of the wall, so that in thatregion a more or less securely adhering layer of crystals forms. Thislayer of crystals must be continuously removed by means of the scrapersand mixed with the remainder of the mass of crystals.

In the known forms of embodiment of the apparatus dealt with here, theinner surface of the heat exchange tube is continuously scraped, theapplication pressure of the scraper blades or the helical element beingalways identical. This has the disadvantage that it is not possible toinfluence individually the application pressure in accordance with theparticular crystallization conditions obtaining.

SUMMARY OF THE INVENTION The problem underlying the invention is inproviding an apparatus wherein the application pressure with which thescraper blades or other scraper means abuts against the inner wall ofthe heat exchanger, can be adjusted to an optimum value and, ifnecessary, also individually regulated.

This problem is solved with a doublewalled tubular heat exchanger of thetype described hereinbefore which is, according to theinvention,'characterized in that for pressing the scraper blades againstor lifting them away from the inner wall of the heat exchanger there arearranged between the blade and the shaft pneumatic or hydraulicadjusting devices whose pressure medium chambers communicate through theinterior of the shaft with an external pressure source. This arrangementmakes it possible to press the scraper blades more or less stronglyagainst the wall, depending on requirements, or to lift them away fromthe wall completely if it is not desired to scrape the inner wall. It isalso possible with the apparatus proposed to scrape the inner wall onlyperiodically at sclectable intervals of time, the intervals beingadjusted or preselected, for example, by suitable control apparatus.

A preferred form of embodiment of the apparatus according to theinvention is characterized in that the blade holders are mounted to bedisplaceable in the radial direction of the heat exchanger in the termsof a helical element supported by the central shaft. The helical elementin this form of embodiment has the task of conveying the materialaxially through the apparatus and at the same time supporting thescraper blades which are radially displaceable.

It is particularly advantageous if a plurality of blade holders arearranged in the longitudinal direction of the heat exchanger, each beingassociated with a pneumatic or hydraulic adjusting device whose pressuremedium chambers communicate with the outside individually or jointlythrough the interior of the shaft. In this way it is possible to scrapewith varying application pressure in the various sections of theapparatus, thus permitting optimum utilization of the apparatus and theenergy used.

It is also proposed to arrange the blade holders which follow oneanother in the longitudinal direction so that they are offset in eachcase by relatively to one another, thus achieving the result that thescraping means bear on the inner wall of the heat exchanger in everyposition, which is advantageous more particularly in the case ofapparatus of great length.

In order not to scratch the delicate, and in many cases polished, innersurface of the heat exchanger by the contacting helical element slidingduring revolution, the helical element can be provided at its outerperiphery with cushions of a suitable material, for examplepolytetrafluorethylene or the like. These cushions can be in the form ofstrips which are inserted interchangeably in appropriately shapedextensions on the outer edge of the helical element.

The adjusting devices for pressing-on and lifting-off the scraper bladesare preferably constructed as closed bellows chambers. The material ofwhich the bellows or diaphragms are produced will depend on the natureof the material being processed in the apparatus, and more particularlyon its corrosive properties. But it must also be borne in mind that thefully crystallized pulp subjects the bellows surface to wear, so thatthis must be as abrasion-resistant as possible. It is most advantageousto use metal bellows for the adjusting devices. It may be advantageousto connect the two end plates of the be]- lows chambers withtelescopically interengaging tubes which are displaceable relatively toone another and which in their lower region comprise radially directedthrough-flow apertures for the pressure medium.

As pressure medium there may be used primarily inert gases, for examplenitrogen or the like. Gases have the advantage over liquids that ifthere are slight leakage losses the material being processed is notfouled. Also they have the advantage that the scraper blades abutelastically against the inner wall of the heat exchanger owing to thecompressibility of the gases. On the other hand, when using liquids aspressure transmitting means it is possible to produce relatively highapplication pressures.

In another form of embodiment of the adjusting device according to theinvention, this has a cylinder and piston whose pressure medium chambersnearest the shaft communicate with the outside through the interior ofthe shaft and wherein the chambers nearest the heat exchanger each havea spring, preferably a helical spring subjected to pressure. In thisform of embodiment, the scraper blade is pressed by means of thepressure medium against the inner wall of the heat exchanger. At thesame time, the spring is also compressed, so that its stored energy isused, when the application pressure is relaxed, to lift the scraperblade off the inner wall of the heat exchanger again.

BRIEF DESCRIPTION OF THE DRAWING The invention will be explained in moredetail hereinafter with reference to the accompanying drawings.

In the drawings:

FIG. I shows a diagrammatic cross section through a form of embodimentof the apparatus according to the invention;

FIG. 2 shows a diagrammatic longitudinal section through another form ofembodiment;

FIGS. 3 and 4 show fragmentary views on a larger scale from crosssections similar to FIG. I.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The heat exchanger shown inFIG. 1 comprises a housing having an outer tube 1 in which an inner tube2 is arranged concentrically. A hollow shaft 3 is arrangedconcentrically in said inner tube 2. A tubular chamber 4 is used forconducting a coolant therethrough, and the likewise tubular space 5 forreceiving the material to be cooled. The chamber 4 is connected byconduits (not shown) to a coolant source and a coolant dischargeconduit. Depending on the nature of the material being dealt with, watermay be used as the coolant, being conducted for example in a closedcircuit with interposition of a suitable cooling device.

The material to be cooled is introduced into the tubular chamber 5through means which are also not shown, because they are known, andmoved by means of a helical element, that is a conveyor screw 6 which isconnected fast .to the shaft 3 rotating in the direction of the arrow 7.For the continuous cleaning of the inner surface of the tube 2, thereare arranged in the interior of the chamber 5 scraper blades 8 which aresupported by blade holders 9. In order to enable the blades 8 to bepressed to a greater or lesser extent against the inner surface of thetube 2, or to be removed entirely from the said surface there arearranged between the blade holders 9 and the shaft 3 hydraulic orpneumatic adjusting devices 10 whose pressure medium chambers 11communicate with the outside by means of openings 12 to which areattached appropriate conduits 24 extending through the interior 13 ofthe shaft 3. At the end of the apparatus, these pressure conduits areconnected through rotary coupling 25 to controllable pressure mediumsource 26 adapted to be switched on and off.

In the special form of embodiment shown in FIG. 2, the blade holders 9are mounted to be displaceable in the radial direction of the heatexchanger in the turns of the conveyor screw 6 supported by the shaft 3.This arrangement makes it possible to dispense with special bearingswhich would otherwise be necessary if in one constructional form therewere no screw 6 to serve as a conveying worm. Advantageously, aplurality of blade holders 9 are arranged one behind the other along thescrew 6 in the longitudinal direction of the heat exchanger in such anarrangement that each is offset by 90 relatively to adjacent holders,and each has a pneumatic or hydraulic adjusting device 10 associatedwith it.

The pressure medium chambers of these adjusting devices can be made tocommunicate individually or jointly with the outside as describedhereinbefore. If the pressure medium chambers communicate with theoutside individually, as shown, it is possible for each blade to bepressed individually against the inner wall of the tube 2 or removedtherefrom. Each adjusting device 10 is connected by its individualconduit 27, 28 and 29 through coupling 30 to a corresponding pressuresource 31, 32 and 33 respectively. These pressure sources may beindependently controlled.

In this way the apparatus can be adapted in the optimum manner to theparticular purpose in view. The screw 6 is provided at its peripherywith U-shaped holding elements 22 in which plastics material strips 23consisting, for example, of polytetrafluorethylene, are interchangeablyset.

FIG. 3 shows an embodiment wherein the adjusting device 10 has acylinder 14 in which a piston is arranged. The

piston is connected by means of a rod 16 to the blade holder 9, so thatits movement is transmitted to the blade holder. In the example shown inFIG. 3, the pressure medium chamber 1 1' is connected, through theopening 12, to the interior 13 of the shaft 3. In the chamber 11" thereis arranged a helical spring 17 which is compressed when pressure mediumflows into the chamber 11 and the piston 15 is raised in consequence. Asa result, energy is stored in the spring 17 and this energy is used,when the pressure in the chamber 11' is relaxed, to lift the bladeholder 9 with the scraper blade 8 away from the inner surface of thewall 2.

In FIG. 4, the adjusting device 10 has a bellows chamber 18 which isarranged between two end plates 19 and 19. The end plates are connectedto telescopically interenga ing tubes 20, 0' which are displaceable relalvely to one anot er and comprise radially directed throughflowapertures 21 for the pressure medium. In this case the pressure mediumflows from the interior 13 of the shaft 3 into the tube 20 and fromthere through the apertures 21 into the interior of the bellows 18. Inthis way easy action on the entire interior of the bellows 18 isensured, and at the same time it is ensured that the blade holder isguided in stable manner by the telescopically interengaging tubes 20,20'. This additional guiding of the blade holder at its ends in additionto the guiding mentioned hereinbefore may be advantageous if in oneapparatus particularly long blade holders happen to be used.

Iclaim:

1. A heat exchanger for cooling material by means ofa cooling medium,having a tubular housing confining a space for said material to becooled; said housing having an inner wall and an outer wall, said wallsdefining a space for said cooling medium, a rotatable shaft coaxiallyarranged in said housing; scraper blades movably mounted on said shaftand movable into engagement with the inner surface of said inner wall;fluid actuated adjusting means having a chamber for a pressure mediumand being arranged between at least one of said blades and said shaft; asource for said pressure medium, said shaft including conduit meansconnecting said chamber with said source.

2. Heat exchanger according to claim 1, in which said shaft comprises aconveyor screw for conveying said material to be cooled in the directionof the axis of said shaft; said scraper blades being movably mounted onsaid conveyor screw.

3. Heat exchanger according to claim 2, in which said conveyor screw isprovided at its outer edge with outwardly open holding strips andcushion strips inserted into said holding strips.

4. Heat exchanger according to claim 1, in which in the direction of theaxis of said shaft, there are arranged a plurality of said scraperblades and a plurality of said adjusting means; said conduit meanscomprising a single conduit communicating with said adjusting means.

5. Heat exchanger according to claim 1, in which, in the direction ofthe axis of said shaft, there are arranged a plurality of said scraperblades and a plurality of said adjusting means; said conduit meansincluding conduits separate from each other and each communicating witha single adjusting means said source for fluid pressure medium comprisesa plurality of sources, one connected to each conduit.

